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Preventive detention is an imprisonment that is putatively justified for non-punitive purposes.
A related, but different form of detention, is detention of suspects or remand. In contrast to preventive detention, detention of suspects must quickly be followed by a criminal charge (or happen after the charge).
In most jurisdictions, people suffering from serious mental illness may be subject to involuntary commitment under mental health legislation. This is undertaken on health grounds or in order to protect the person or others. It does not strictly speaking constitute a form of preventive detention, because the person is detained for treatment and released once this has proved effective.
Australian laws authorize preventive detention in a variety of circumstances. For example, mandatory detention in Australia (a form of immigration detention) is applied to asylum seekers who arrive in Australian water or territory, until their status as an asylum seeker is established.
In Costa Rica, the 1998 Criminal Proceedings Code allows for a normal pre-trial "prisión preventiva" or remand of 12 months if the person is considered a "flight risk", but if the case is declared "complex", it can be increased to up to three years and a half of imprisonment without conviction, or even more in some cases. As of 23 May 2013, over 3,000 people were in pre-trial detention.
The police can detain people for 6 hours without involving the courts or pay compensation for wrongful arrest. In relation to the ongoing gang war in Copenhagen between the biker gangs and second generation youth gangs it has been suggested to extend the 6 hour limit to several weeks. Before the Copenhagen Climate Council a new set of emergency laws was introduced allowing the police to detain people for up to 12 hours without charging them for a crime. Critics fear that they will remain as permanent laws when the summit is over.
In Germany, "preventive detention" (German: Sicherungsverwahrung, §66 Strafgesetzbuch) has a similar meaning to that in New Zealand. Sicherungsverwahrung can only be imposed as part of a criminal sentence, and it is handed down to individuals who have committed a grave offence and are considered a danger to public safety. It is an indeterminate sentence that follows a regular jail sentence. To assure the suitability of the preventive detention, it has to be reviewed every two years to determine the ongoing threat posed by the individual. Preventive detention is typically served in regular prisons, though separated from regular prisoners and with certain privileges.
The Sicherungsverwahrung is usually imposed in the original verdict, but can be imposed later under certain circumstances. This practice of subsequent incapacitation orders was ruled a violation of Art 7 of the European Convention on Human Rights by the European Court of Human Rights. Subsequently a huge discussion in Germany over the handling of this verdict occurred. In reaction to this the Federal Constitutional Court of Germany issued a verdict on Sicherungsverwahrung in May 2011, deeming it unconstitutional.
In India, preventive detention can be extended for only six months. After three months, such a case is brought before an advisory board for review.
Preventative detention in India dates back to British rule in the early 1800s, and continued with such laws as the Defence of India Act 1939 and the Preventative Detention Act 1950.
The controversial Maintenance of Internal Security Act was enacted by Indian parliament during Indira Gandhi prime ministership in 1971, however it was amended several times during national emergency (1975-1977), leading to human right violations. It was subsequently repealed after Indira Gandhi lost the election in 1977, and the new government took over.
In Malaysia the Internal Security Act 1960 (ISA) is a preventive detention law in force. The legislation was enacted after Malaysia gained independence from Britain in 1957. The ISA allows for detention without trial or criminal charges under limited, legally defined circumstances. The ISA is invoked against terrorism activity and against anyone deemed a threat to national security. On 15 September 2011, Najib Razak, the Prime Minister of Malaysia, said that this legislation will be repealed and replaced by two new laws. The ISA would only be repealed in March 2012.
On 17 April 2012, a new law known as the Security Offences (Special Measures) Act 2012 (SOSMA) was approved by the Malaysian Parliament as a replacement for the ISA. It was given the Royal Assent on 18 June 2012 and gazetted on 22 June 2012. 
In New Zealand, "preventive detention" is an indeterminate life sentence, and is handed down to individuals convicted of violent and/or sexual crimes (such as sociopathic murderers, serial rapists or recidivist pedophiles) where it is likely that the offender will reoffend if released. Such individuals will only receive parole if they can demonstrate they no longer pose a threat to the community. In October 2010, a total of 269 prisoners in New Zealand were serving terms of preventive detention.
Preventive detention has a minimum non-parole period of five years in prison, but the sentencing judge can extend this if they believe that the prisoner's history warrants it. Prisoners on preventive detention are very rarely, if ever, released, and generally persons given the sentence are kept in prison for life. Currently only 16 of the 269 persons serving sentences of preventive detention are on parole.
The longest non-parole period on a sentence of preventive detention is one of 30 years, being served by William Bell, in 2003, he was sentenced to a minimum non-parole period of 33 years for killing three people in Auckland in December 2001. The sentence was later reduced to 30 years.
In 2002, Bruce Thomas Howse was sentenced to life with a 28-year non-parole period for the murders of his two stepdaughters in Masterton on December 4, 2001. Alfred Thomas Vincent has been in prison on preventive detention since 1968 and was still there as of 2014.
Aaron Rhys McDonald who raped and murdered a Christchurch woman and attacked two foreign hitchhikers on the West Coast has been sentenced to preventive detention for a minimum non parole period of 21 years.
Under Apartheid, the government of South Africa used preventative detention laws to target its political opponents. These included, notably, the Terrorism Act of 1967, which gave police commanders the power to detain terrorists—or people with information about terrorists—without warrant.
England and Wales used to have provisions, introduced by the Labour Government in 2003, to deal with dangerous offenders similar to what is used in Canada. However, the Legal Aid, Sentencing and Punishment of Offenders Act 2012 abolished what was called Imprisonment for Public Protection (IPP) without replacement, although offences committed prior to the coming into force of the 2012 Act may still trigger IPP.
In the United States, the Sixth Amendment to the United States Constitution guarantees the right to "a speedy and public trial". Thus, arrested persons may not be held for extended periods of time without trial. Convicted persons can be held indefinitely as a Dangerous Offender.
- Preemptive arrest
- Administrative detention
- Arbitrary arrest and detention
- Civil confinement
- Indefinite imprisonment
- Anti-Terrorism Act 2005 (Australia)
- Criminal Law (Temporary Provisions) Act (Singapore)
- Internal Security Act (Singapore)
- "In Costa Rica 17 persons ordered daily to preventive detention". QCostarica.com. Q Media. 30 June 2013. Retrieved 2 May 2015.
- The police law (Danish), Web page of the Danish police
- S vil sætte bandekrigen bag tremmer, by Bente Lund, Denmarks Radio, February 22, 2009 (Danish)
- Hårdt politisk opgør før Folketinget sagde ja til lømmelpakken, by Jens Ringberg, Denmarks Radio, November 26, 2009 (Danish)
- Lømmelpakken bekymrer dommerne, Politiken, November 13, 2009 (Danish)
- A. Faizur Rahman, "Preventive detention an anachronism", The Hindu, 7 September 2004.
- USA., International Business Publications, (1 May 2001). India: Foreign Policy & Government Guide. Int'l Business Publications. pp. 34–. ISBN 978-0-7397-8298-9.
- Saxena, Priti (1 January 2007). Preventive Detention and Human Rights. Deep & Deep Publications. pp. 99–. ISBN 978-81-7629-992-3.
- Internal Security Act to be abolished, says Najib, 15 September 2011, Bernama.com.
- "ISA to be repealed in March". Free Malaysia Today. 30 September 2011.
- "Security Offences (Special Measures) Act" Retrieved 11 February 2013
- Vance, Andrea (8 October 2010). "Preventive detention rates rocket". Stuff.co.nz. Retrieved 4 November 2011.
- Mussen, Deidre (3 November 2014). "Child molester's case might go to UN". The Dominion Post. Retrieved 28 April 2015.
- Jonathan Cohen, "1967 Terrorism Act, No. 83 of 1967", South African History Online.